"How could I have missed it? The answer was right in front of me all along!"

Connecting the Dots

Whenever a creature you control attacks, exile the top card of your library face down. (You can't look at it.)
{1}{R}, Discard your hand, Sacrifice this enchantment: Put all cards exiled with this enchantment into their owners' hands.

Murders at Karlov Manor

Whenever a creature you control attacks, exile the top card of your library face down. (You can't look at it.)
{1}{R}, Discard your hand, Sacrifice Connecting the Dots: Put all cards exiled with Connecting the Dots into their owners' hands.

Murders at Karlov Manor Promos

Each Connecting the Dots you control has its own set of face-down exiled cards. Connecting the Dots's last ability puts only those cards into your hand, not those of any other Connecting the Dots.

If Connecting the Dots leaves the battlefield before you activate its last ability, any cards exiled by its triggered ability remain exiled face down for the rest of the game. (You still can't look at them.) If you somehow return the same Connecting the Dots to the battlefield, it will be a different object with no connection to those face-down cards.

You can pay the cost of "discard your hand" even if your hand contains zero cards.